President Barack Obama's nominee to head the Food and Drug Administration is facing friendly fire, with Democratic presidential candidate Bernard Sanders and Massachusetts Democrat Edward J. Markey both placing a hold on the nomination.

Sanders said Tuesday that Robert Califf, currently serving as deputy commissioner at the FDA, is too closely tied to the pharmaceutical industry. Califf ran a research operation while at Duke University that received funding from that industry. "At a time when millions of Americans cannot afford to purchase the prescription drugs they require, we need a leader at the FDA who is prepared to stand up to the drug companies," Sanders, an independent from Vermont who caucuses with the Senate Democrats, said in a statement. "We need someone who will work to substantially lower drug prices, implement rules to safely import brand-name drugs from Canada and hold companies accountable who defraud our government."

In his statement, Sanders said he concurred with concerns raised by Markey about the FDA's approach to addressing the scourge of opioid addiction. Markey announced a hold on the nomination Monday.

"Expert after expert has warned about the real world dangers of abuse of and dependence on these new supercharged opioid painkillers, but the FDA has willfully blinded itself to the warning signs," the Massachusetts senator said in a statement. "The FDA needs to commit to shift the way it approaches and evaluates addiction before I can support Dr. Califf's nomination. Until it does, we will continue to see this tsunami of opioid overdoses engulf family after family."

A hold on a presidential pick is not unexpected from an opposing party. But two holds in two days from the president's own party signals trouble for the nomination. Obama named Califf to take the top job in September, and initial predictions were that the nomination would sail through.

The Democrats' objections come after Republican Sen. Lisa Murkowski of Alaska had already lodged her own hold on the nomination. Her concern lies with the FDA's treatment of genetically-modified salmon, which critics refer to as "Frankenfish."

As of Tuesday, a Murkowski aide said, the FDA had not provided answers to questions the senator raised. She placed the hold on the nomination on Jan. 13, just after Califf's nomination was reported out of the Senate's Health, Education, Labor and Pensions Committee.

A Republican aide indicated later Tuesday that, at least as far as the holds from Sanders and Markey were concerned, GOP leadership intended to push forward.

"Sens. Markey and Sanders seem to have forgotten their fervent support for breaking the rules of the Senate to change the rules of the Senate on nominations. Dr. Califf will get his opportunity for a majority vote to confirm his nomination in the near future," the aide to a GOP senator said.

That's a reference to changes in the Senate's precedents pushed through by then-Majority Leader Harry Reid, D-Nev., allowing a simple majority to break a filibuster of most nominations, including for the FDA post. That action would overcome any holds.

Contact Lesniewski at NielsLesniewski@cqrollcall.com and follow him on Twitter @nielslesniewski.